Disposable heat wraps have become a popular application of applying heat to relieve discomfort of temporary or chronic body aches and pains. These disposable heat wraps typically comprise an exothermic composition for generating heat, wherein the exothermic composition typically comprises metal powder, salts, and water that allows the exothermic composition to release heat upon oxidation of the metal powder. The heat treatments provided by the disposable heat wraps have been found suitable for treatment of aches and pains associated with stiff muscles and joints, nerve pain, back pain, rheumatism, and the like.
Disposable heating devices can provide sustained heat for periods of from about one hour to about twenty-four hours, and are described as being less messy and more convenient to use that other conventional heat sources such as whirlpools, hot towels, hydrocollators, heating pads and elastic compression bands. Disposable heating devices are further described as satisfactory devices that can maintain consistent and controlled temperature, see for example U.S. Pat. No. 5,918,590 where it is disclosed that heat cells based on specific iron oxidation chemistry are suitable for incorporation into disposable body wraps to provide sustained temperature resulting in consistent, convenient, and comfortable heat application for treating temporary or chronic pain.
It has been found, however, that while sustaining temperature for periods of up to about twenty-four hours, the consistency of the sustained temperature can be improved. One approach of enhancing exothermic reactions is the incorporation of carbon materials such as activated and non-activated carbon materials. Other approaches include the addition of water-retainers or water-holding materials. See for example, the disposable heating devices disclosed in U.S. Pat. Nos. 6,436,126; 6,099,556; and 5,233,981. See also the heating devices disclosed in U.S. Published Patent Application Nos. 2004/0042965 and 2004/0178384.
One specific example of an exothermic composition comprising a water-absorptive polymer is disclosed in U.S. Patent Application Publication No. 2002/0020406. This publication discloses a united exothermic medium wherein an exothermic agent is mixed with a water-absorptive polymer and then the agent/polymer mixture is pressed together with alcohol, a crosslinking agent, or a plasticizer at a certain pressure, to be thereby united.
Despite the disclosures in the art of disposable heating devices comprising exothermic compositions, the need still exists for a specific heating device that comprises an exothermic composition that provides for controlled and sustained temperature throughout the heating period. It is known that the thermal performance of heat cells is highly sensitive to moisture level, and a typical heat cell can comprise water concentrations at or above about 27% to sustain the heating temperature of the heat cell. However, the inclusion of high concentrations of water at levels of about 27% or above can result in slower than desired initial heating temperatures. Therefore, the ability to rapidly reach the desired temperature for a therapeutic benefit and the ability to sustain the temperature are difficult to achieve.
Moreover, current heating devices contain exothermic compositions that are highly prone to segregation effects. It is believed that the particle size differences between the compositional components can contribute to particle segregation. For example, heating devices containing an exothermic composition that comprises water-retainers (e.g., vermiculite, wood flour, absorbing gelling material) in combination with iron powder and carbon have a tendency to segregate. Typically, the particle size of the water retainer is quite large when compared to the iron and carbon particles. For example, current heating devices can comprise exothermic compositions wherein the mean particle size of the water retainer to iron particles is often 10:1 or more, resulting in high particle segregation.
Changes in particle mix composition due to segregation could lead to product thermal performance that is less than optimal and/or different from the intended design. Thus, maximum reaction efficiency is typically not achieved with current heating devices since excess exothermic composition is needed to compensate for particle segregation effects. These heating devices typically comprise heat cells that have relatively large volumes which allow them to accommodate for the excess exothermic composition.
It has been found that heat cells comprising an exothermic composition that comprises an absorbent gelling material are especially effective in rapidly reaching initial heating temperatures as well as being effective in maintaining a consistent temperature for periods up to twenty-four hours. When used in select ratios with other compositional ingredients, it has been found that the absorbent gelling material provides for improved heat application in addition to providing for exothermic compositions that resist compositional changes such as segregation. To provide minimal or no segregation effects, the exothermic compositions of the present invention comprise select particle size ratios of absorbent gelling material to iron powder.
The heat cells of the present invention have adaptable physical dimensions which provide for the heat cells to be incorporated into disposable heating devices such as back wraps, knee wraps, body wraps, joint wraps, menstrual wraps, neck-to-arm wraps, and so forth.